Opposition Leader Bill Shorten is facing an internal battle, with Labor MPs urging their colleagues to drop support for asylum seeker processing on Nauru and Papua New Guinea and instead advocate the closure of the two centres.

In a move that will reignite the damaging political debate in the party over asylum seeker policy, West Australian MP Melissa Parke and Victorian MP Anna Burke, the former Speaker, will put the motion to the caucus room on Tuesday.

The move comes just three weeks after Labor immigration spokesman Richard Marles told the National Press Club that he fully supported offshore processing and that the Rudd government should never have dismantled the offshore centres.

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"We support offshore processing at Nauru and Manus Island as a step which has saved lives," he said at the time.

But a copy of a motion cites the death of Iranian asylum seeker Reza Barati, the "inhumane, unsafe and completely unsatisfactory conditions" for asylum seekers on Manus Island and Nauru and a lack of independent oversight of the centres, and the lack of processing of asylum claims in both countries as justification for the move.

It also points out that the policy is inconsistent with the ALP's national platform and argues the system violates Australia's obligations under the UN refugee convention.

The motion calls for Labor to "no longer support the transfer of asylum seekers by Australia to Manus Island or Nauru" and "detention centres in those places to be closed forthwith".

The motion was due to be debated about a month ago but it is understood it was delayed so that it wouldn't clash with Mr Marles' appearance at the press club.

Ms Parke and Ms Burke both declined to comment when contacted by Fairfax Media and it is understood the motion is unlikely to win majority support in the caucus room, with many Labor MPs simply unwilling to re-start debate over an issue that plagued Labor for six years in government.

But Victorian Labor MP Maria Vamvakinou, who will back the motion, said the issue of asylum seekers was "vexed" and the party could not ignore it.

Ms Vamvakinou said that under the Coalition "the boats have stopped but we still have an issue with people who will need protection".

"Nauru and Manus are not sustainable. They have become nothing but a place where people are left and possibly even abandoned," she said.

"The problem doesn't go away with the stopping of the boats. What we need to do is fund a regional solution ... we have to make a really concerted push to work with countries in our region to try and get regional co-operation."

Claire Moore, a Queensland Labor senator, said the treatment of asylum seekers was a "significant issue" within the Labor Party, and had been so since she joined the party in 2001.

"This debate is real, and it's not an easy one," Senator Moore said. "There is a great deal of feeling across the board and [it is] something that members feel strongly about."

The motion comes amid growing concerns about Manus and Nauru and the treatment of asylum seekers.

Last week, a Senate inquiry into violence at Manus painted a picture of chaos in regard to who was responsible for the centre and the lack of accountability during the attacks in February, when at least 69 people were injured.